Ethylene oxide (“EO”) is highly toxic. The US Department of Labor Occupational Safety and Health Administration (“OSHA”) has set stringent guidelines aimed at protecting workers performing operations in an environment potentially contaminated with EO. The Permissible Exposure Limit (“PEL”) for EO has been established at 1.8 mg/m3 (approximately 1 ppm). As a result, effective, low cost means of removing EO from ambient streams of air are needed.
Impregnated, activated carbon is known to strongly adsorb a wide variety of organic chemicals from ambient air streams. Impregnated, activated carbon does not, however, function well under conditions of high relative humidity, (hereinafter “RH”) such as for example greater than about 70 to 80% RH. This is because under conditions of high RH, water vapor is adsorbed by the activated carbon, filling the pores and thereby greatly reducing the adsorption capacity for organic chemical such as EO.
Kruse and Hammer (U.S. Pat. No. 4,813,410) disclose an acidified resin capable of filtering EO. Although the acidified resin is able to very effectively filter EO at up to 50% RH, the performance of the material begins to decrease as the RH is increased past 50%. Although details are not provided, the authors report a decrease in performance as the RH is increased beyond 50%, and “unsatisfactory” performance at 85% RH.
Pollara and Liddle (U.S. Pat. No. 4,612,026) report the use of activated carbon impregnated with copper, silver and chrome employed in a filter to remove EO from streams of air. The authors report that the filter is able to effectively remove EO to sub ppm levels, however, process conditions such as flow rates, atmospheric temperature and atmospheric relative humidity are not provided.
Depending on the environment and environmental conditions, the water content associated with ambient air can vary over a wide range, from less than about 10% to greater than about 80% relative humidity (RH). Although a number of media, such as, for example, activated carbon and resins, are capable of removing EO from dry air, these materials fail to effectively filter EO under conditions where the relative humidity is high (U.S. Pat. No. 4,813,410). Therefore a need exists for a method to remove EO from ambient humid air streams.